1. Field of the Invention
This invention relates to an electronic musical instrument, and more particularly to an electronic musical instrument which has a musical waveshape memory part formed with a variable-stage shift register in each channel register of a non-real time processing system.
2. Description of the Prior Art
In recent digital electronic musical instrument, a key code is generated by a key switch and is assigned to a plurality of channels and the key code and the envelope corresponding thereto are applied to a musical waveshape generator. On the other hand, a tone change is detected by a tone selector from the ON-OFF state of a tone selecting tablet, draw bar switch or the like, a waveshape calculation is carried out by a waveshape calculator, the output from the waveshape calculator is applied to the musical waveshape generator to synthesize the waveshape corresponding to the key code and an envelope is added to obtain an acoustic signal output. Heretofore, two methods have been employed to provide the musical waveshape with an interval in the musical waveshape generator. A first method employs a note clock generator which generates a frequency proportional to a note frequency. Almost all of existing digital organs adopt this first method. A variety of methods have been proposed to produce a clock having the note frequency. However, the circuit of the first method is appreciably complicated and a high clock frequency, for example, 2 to 4 MHz, is required for maintaining the accuracy of frequency.
The second method sets a numerical value called "frequency number", which is proportional to frequency. The numerical value is stored in a frequency generator and accumulated by a decimal counter and an integer counter to use the frequency output as an address of a musical waveshape memory. This method poses the problem that the associate circuits become very complicated and bulky.